Copyright 2012 Scripps Media, Inc. All rights reserved. This material may not be published, broadcast, rewritten, or redistributed.

(CNN) -- A shooting at a Newtown, Connecticut, elementary school has left at least three people critically wounded Friday, the mayor of a neighboring town where the wounded were taken told CNN.

It was unclear if there were additional injuries or deaths at Sandy Hook Elementary School, but the suspected gunman was dead, a source with knowledge of the investigation told CNN's Susan Candiotti.

The three wounded people were in "very serious" condition, Danbury Mayor Mark Boughton told CNN. He couldn't say whether the victims were children. Danbury Hospital confirmed that it was treating three patients from the shooting.

Police have recovered two weapons from the suspect, a Glock and a Sig Sauer, the source said. It's unclear if police killed the suspect.

The Newtown Bee newspaper said one child had been carried out by a police officer and emergency crews had set up triage facilities, expecting additional patients. The Hartford Courant newspaper said one victim had "numerous gunshot wounds."

Aerial images from CNN affiliate News 12 New Jersey showed police officers armed with rifles following a dog into woods near the school.

Other officers, some in tactical gear, stood around the school with guns drawn, CNN affiliate WFSB reported.

A photograph published by the Newtown Bee showed teachers and police leading students out of the building across a parking lot.

One student, a third-grader, told CNN affiliate WTNH that she was sitting in her classroom when police flooded the area.

"We saw police officers and we heard them on our roof and in our building," the girl said.

Some of the children were crying, and others felt they had a stomach ache, she said.

The girl's father told the station the incident was shocking.

"I was pretty shaken up," he said.

All schools in the city were on lockdown Friday as police assessed the situation, state police spokesman Lt. Paul Vance said.

Students were evacuated to a nearby firehouse, the Danbury News-Times newspaper reported.

The first calls came into police around 9:40 a.m., according to media accounts.